How do I get off the mailing list?

Sales catalogs continue to be mailed (snail mail) for 3 years after my business closed. I have called several times, each time being told I would be removed from the list. I just spent the better part of an hour on the phone with 3 different "agents" who told me that I would no longer receive catalogs after 24 hours, or 3 weeks, or 15 days. When I ask to file a complaint, I get the total run-around with no answer. The accents of the "agents" are so thick I've had to have them repeat numerous times. I'm so frustrated! I have purchased 4 computers and 2 printers in the past, but will never buy a Dell again after this experience.